Realization and characterization of XUV multilayer coating for attosecond pulses

High Order Harmonics are generated by ionization of atoms with ultra-intense and ultra-short infrared LASER pulses. Harmonics spectrum bandwidth covers a wide EUV spectral region allowing the generation of attosecond pulses by amplitude and phase modification of each spectral component. Generation of attosecond pulses can be realized by filtering a particular spectral region, moreover, additional time compression can be obtained by the harmonics phase reordering . The realization of broadband multilayers able to reflect and compress attosecond pulses is a crucial point for attosecond research. We have realized multilayers with broadband rectangular reflectivity and negatively chirped phase trend able to comply the high order harmonics phase mismatch. The aperiodic multilayers has been designed by a suitably developed optimization algorithm.. We show the experimental characterization of two Mo/Si broadband multilayer designed for compressing attosecond pulses in the EUV region, they have been characterized at the BEAR beamline of ELETTRA synchrotron. The multilayer phase characterization has been derived using an innovative method based on the total electron yield signal.